


The Glass Box

by Silverskye13



Series: The Bodyguard AU [5]
Category: Undertale (Video Game)
Genre: Claustrophobia, Despair, Its a bad time, M/M, Psychological Torture, Torture, Trapped, but like there's a good ending, okay ? its just a really bad time, these tags are absolutely mortifying
Language: English
Status: Completed
Published: 2019-09-21
Updated: 2019-09-21
Packaged: 2020-10-25 10:54:26
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 4,180
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20723039
Author URL: https://archiveofourown.org/users/Silverskye13/pseuds/Silverskye13
Summary: Originally posted on TumblrDirect sequel toThe Crumbling Wallso I would read that one first if you haven't already!





	The Glass Box

Gaster awoke the next morning to the sound of his cell door opening. The first thing he felt was how sore and cold he was after sleeping on the floor. It had been a rough, stressful, cramped night and he could feel the coolness in the air all the way down to his marrow. The next thing he felt was blinding terror as hands clenched around his shoulders and dragged him to his feet. There was no telling him to stand, or even waiting for him to gather his senses. There was just him moving against his will across the concrete floor before his eyes could rightly register the images around him.

The cell was still there, though now he was leaving it. The metal bars, the black ceiling, the cold stale grit that made the place smell like a tomb. And there was a soft light burning, flickering, looking dismally up at Gaster as he was escorted out.

No not dismally. Blankly. Hollow. A brick wall of a stare that turned itself impassively to the monster that opened its own cell door. Grillby let himself be dragged as well. Had to have let it happen, because Gaster had never seen the elemental so resigned to something happening before, and it terrified him. Where was the struggle? The spite? For as long as he was able he searched Grillby for it. For some ghost of a _hint _of a plan in the fire elemental’s eyes. For anything. Anything at all.

But there wasn’t. _Of course_ there wasn’t. He already knew that. And with nothing else to do but try and keep up with the brisk pace his captors kept, Gaster trod on. 

The hallways here were empty, and just as grey and desolate of the cell he’d been in. Gaster had to wonder if this entire wing of… _wherever _they were… was made specifically for occasions like this. For those fabricated moments when hope was forced to its lowest, where wills were bent, reshaped, repurposed. It was dreadfully monotonous, and quiet. He wanted to talk to fill the silence, to stop the nervous crawling he felt in his soul, the shiver in his breath. To stop him feeling like a deer trapped in oncoming headlights.

There was noise up ahead. Talking. Gaster hazarded a glance back over his shoulder to Grillby for recognition or… reassurance… but Grillby hardly seemed to be paying attention. His eyes were trained somewhere on the floor, boredly. Detachedly. Like his mind was somewhere else.

It probably was.

If Gaster were smart, he’d be doing the same thing. He’d be… doing mental gymnastics over the advice Grillby had given him the night before. Thinking about the elemental and all his shortcomings. He’d be… thinking about how quiet Grillby was and how maddening the silence was sometimes. He’d be thinking about how overbearing Grillby was, constantly fussing over him. Worrying over him and neglecting himself in the process. He’d be thinking about how _terrified _he always was when something happened that he was going to get Grillby killed.

Like he was now.

He was getting Grillby killed. 

This was it.

A door opened itself up ahead, and Gaster found himself on the verge of panic. Never in his life had he ever wanted to _run _so badly. Something bad was about to happen and there was nothing he could do about it. All he could do was wait. And walk.

A second door opened. Two rooms side by side. Gaster found himself walked past the first and into the second, and he cast one last fleeting look in Grillby’s direction before he was shoved in.

But he found, oddly, they weren’t separated. Not _completely_.

The room he entered was a bit like an interrogation room from a police station. It was dark and mostly empty save for a few chairs - and one wall was made nearly entirely of glass. And so, as Gaster was unceremoniously tossed into his room and left, he watched them toss Grillby in his room as well. Grillby’s room was equally barren - though Gaster noticed instead of a few chairs, there was a simple glass box in the middle of the room. It was an odd fixture, long but only a few feet tall. There was some sort of hinge on the side so it could open, and a seal around the top - the lid? - to keep it fixed tightly in place. Gaster had never seen the make of it before. Things _like _it surely, but smaller. It looked like something he might use to test an object in a vacuum - though thank heavens there seemed to be no allowance in this glass box for the air to be removed. No, aside from looking jarringly strange in the empty room… it was just there.

And their guards left them, and just like that, they were alone.

Gaster hugged himself pathetically and watched Grillby through the glass, trying not to act as skittish as he felt. He glanced around the room a few times looking for… anything of note aside from the chairs and the glass pane and coming up short. He wondered distantly if glass would be easier to melt than whatever the bars of their cell was made of? He knew nothing of the melting point of glass. Not that it seemed Grillby would be staging any escape attempts any time soon. 

“U-uhm-”

“You’re not going to like this,” Grillby cut him off abruptly, his gaze trained on the glass box. There was an instant where Gaster thought he saw something _finally _register on the elemental’s face, a flicker of emotion, gone too quickly for Gaster to see what it was. 

Gaster laughed nervously, “I thought… you know… I already knew that.”

“Yeah,” Grillby rubbed the back of his neck, worried, and the simple gesture sent a twinge of nervousness all the way down Gaster’s spine. He didn’t know what that meant, and it scared him, “You remember what I said about pretending you’re somewhere else.”

“Yes but-”

Grillby stiffened at about the same time Gaster heard a click at the door. Through the glass Gaster watched as the door to Grillby’s room opened and in stepped a monster Gaster had never seen before. 

He was a tall, wiry creature, crowned with a mane of cleanly kept feathers and two long spirals of twisting horns that arched backwards gracefully from the top of his head. He dwarfed Grillby easily, standing a head taller than him even without the twisting horns and bristled mane, but his movements were fluid and smooth like silk, comfortable and graceful instead of the lumbering Gaster had come to expect from most monsters that size. He wore a cleanly tailored suit, _expensive_, if Gaster placed it right. It looked like something Gaster would see in shops hedging the castle square, all shimmering fabric and sharp edges. And the monster himself exuded a sort of power, like an aura that washed out from him with his breathing. A sort of overbearing magic that Gaster had only ever felt while standing near the King. Suddenly Gaster understood how the creature could gather so many lackies to work for him. The creature’s presence was attractive and overbearing even through the thickened glass.

This was a boss monster. 

Behind him entered a pair of what Gaster would simply call henchmen, muscle-bound monsters with grim snarling faces and a constant air of bristled magic. There was a glimmer about their clothing, some sort of magic - likely fireproofed - and a color like ice reflected in their eyes. And standing before them, looking smaller and smaller it seemed the longer Gaster watched, was Grillby. Still stoic and unperturbed as ever, watching the figures with little more than a raised eyebrow.

“Hello again gentlemen,” Grillby said casually, as though he were talking to passing strangers on the street, “We must stop meeting like this.”

The boss monster’s mouth curled in a smile, “Nothing phases you at all does it?”

Then he turned his gaze on Gaster, and the skeleton found himself startling backwards a step. Instantly he was ashamed at it. Wasn’t he supposed to be… staying strong or something? Spiteful resistance and all that fanfare? And here nothing had happened yet and he was cringing away. 

But he couldn’t help it. He wasn’t… he wasn’t made for this and he knew it. He wasn’t a hero or anything. He was just in over his head.

“Doctor Gaster, I’ll offer you a final chance,” the boss monster hummed with a lilting voice, playful almost, “Help me with my little… barrier breaking project. And he goes free. Well… not _entirely _free I suppose. We must keep him out of trouble. But he’ll be safe. You want that, don’t you?”

It was simple. It was _so simple_. Of _course _he wanted Grillby safe, with every bit of his terrified soul. But Gaster looked at Grillby, and the elemental only inclined his head. A small gesture, reiterating one more time his aloofness. That he’d already come to peace with this whole affair and that Gaster should as well. And Gaster felt a tenseness in his soul like a fist in his chest, so much he could feel it through his ribs and his marrow. This was bigger than them, right? That’s what he was supposed to believe. He couldn’t - he couldn’t just -

“Very well,” the boss monster hummed again, gaze snapping to Grillby, “Let’s get to your incentive then, shall we?”

The two lumbering monsters stepped further into the room, brushing roughly past Grillby as they went and right up to the glass box. A box Gaster only belatedly realized was… entirely too _Grillby _sized. He fidgeted with one of his knuckles nervously, still at a loss for what was going on. He was too panicked to - his mind was racing itself in terrified circles and all he could do was fidget and stand. He just didn’t know -

“Doctor Gaster,” the boss monster said, that lilting voice curling past smiling teeth, “How much have you ever played with fire?”

“I-i-i don’t -”

“Oh, I’m sure you know _exactly _what I’m talking about,” the boss monster wrapped an arm around Grillby’s shoulders, and for the first time since they’d entered the room, the elemental looked _truly _uncomfortable. His flame for a moment flickered green, and a disgusted frown curled across his face, “Have you ever lit a candle?”

Gaster looked from Grillby to the monster and back again, “I-”

“And put a glass over it, just to see what would happen?”

Gaster blinked, and he blinked again. And slowly his hand slipped up to cover his mouth.

“See?” the boss monster grinned happily, “I _told _you. Everyone has heard of this little parlor trick, haven’t they?”

With a sudden shove, the monster sent Grillby staggering towards the glass box and its now open lid. Grillby looked down at it for a moment, hesitating.

“Oh go on, try it out,” the boss monster hummed, “I had it made _just _for you.”

Grillby cast a glance back up at the monster, pausing just long enough it seemed for the hulking creatures with him to lose their patience. With a snap of motion one grabbed Grillby by the collar, and with a fierce shove, threw him inside. Grillby tumbled in with a startled grunt, and then scowled, but whatever comeback he began to say was cut off abruptly as the lid slammed shut.

And suddenly Gaster was staring at what looked entirely too much like a coffin made of glass.

“So, the interesting thing about fire, and _fire monsters_,” the boss monster said pacing a little closer to Grillby and smirking down at the trapped elemental, “Is that they need oxygen to stay lit, don’t they?”

Gaster could feel his breaths hitching faster in his chest. Oh gods, he was going to cry. Oh _gods _he didn’t know what to do-

“_Don’t they, _Doctor?”

Gaster screwed his eyes shut and looked away, but in a shuddering voice he managed, “Y… yes.”

“Ah, so you _can _answer me,” Gaster was really growing to hate that loathsome voice, “I’d thought for a moment I’d struck you speechless, and wouldn’t _that _put a damper on things? Now, another interesting thing about fire is, well, it burns oxygen constantly. And when you put a cup over a candle - or a fire in a box, well it can’t really get that anymore, can it?”

A soft, wheezing and painful noise writhed itself past Gaster’s teeth. An involuntary thing that ripped free of him while he breathed and tried his _damnedest _not to cry. And it wasn’t working. He was just shaking harder, and his jaw hurt from how tense it was, and he had never felt so _helpless _in his _life_.

“Doctor, you’re not paying attention,” the voice was _close_, far too close. No longer muffled by the glass wall, and Gaster _jumped_ as he opened his eyes and the boss monster was standing beside him, _towering _over him. That smug smile still firmly in place, “I thought you were a _scientist_, dear. Don’t you like my little experiment?”

Gaster gaped at him to shocked and overwhelmed to do much more than stare. But he cringed when the monster reached out one of his clawed hands and placed it on his shoulder, gently. Surprisingly, stupidly gently, and turned Gaster to face the room where the box lay. Where _Grillby_ lay. And for a moment, Gaster watched and could almost convince himself nothing was wrong. That the box was _flawed_ somehow, and the elemental was simply biding his time in there, waiting patiently.

But the color of his fire was different. Subtly at first. A tinge of orange where there should be yellow. A tinge of red. A flicker smaller than it should be. Grillby for his part was still doing his best to look bored, staring silently at the roof of his coffin. But there was a hard line set in his expression, a tenseness around his eyes. A stiffness in his shoulders. And Gaster saw the elemental give a huff, a deeper breath of air maybe, or a sigh? But black smoke curled with it, and Grillby winced.

And that was all Gaster needed.

“Let him out,” he said quietly, stammering, stumbling over the words so badly he could hardly understand them himself, “P-please.”

“What? And ruin the fun?”

“Let him out!” Gaster said louder, a bit more composed, almost _angry _if he weren’t so pathetically scared. He took his eyes off Grillby for an _instant_ to glare mightily at the boss monster - and was slammed into the glass by the creature’s strong hand pressed against his shoulder blades. 

“No,” he hummed, “I don’t think I will.”

And Gaster found himself staring again, pushing back against the hand behind him but unable to move, and watching as if by some horrible magic Gaster’s looking away had sped everything up. There was no yellow left in Grillby’s flame, just orange turning to red and burning lower. And every breath the elemental took was smoke, and it looked _painful_. Like his every breath was a wince. And worst of all it seemed to Gaster, he still refused to look in his direction. Grillby was more concerned with the intricacies of the ceiling and his own crumbling facade.

“How long do you think he can stay in there, do you think?”

“S-s-sir please-”

“Three minutes? Five minutes? Until he passes out anyway, I’m sure,” he hummed thoughtfully, “And then what will happen, do you think, Doctor? Got a sound hypothesis for me? Do you think he’ll smolder in there for a while before he turns to dust?”

“Stop it! Please!”

“Well… I suppose… _hmm_…” the boss monster spoke slowly, _painfully slowly_, like he had all the time in the world to just stand there and watch as Grillby suffocated in that stupid box and Gaster writhed and cried pathetically beneath his claws, “Well, I suppose, you didn’t really say _no _when I asked you for help in that little project earlier, did you?”

A strand of hope, so thin and frail but Gaster clung to it the instant he had it, “No I didn’t - you - you didn’t let me - I -!”

“Oh, but you hesitated an _awful _long time.”

“I-i-i didn’t know what I was thinking,” Gaster said quickly, grasping at phrases and half-formed thoughts, his only goal to just make the horrible situation in front of him stop. _Stop_. Stop before Grillby burned any lower or coughed up any more smoke, “I-it was so generous of you t-to ask me to be a part of - and the barrier needs to come down -”

“Of course it does.”

“And - and it will! It’s - but it’s - but you want -”

“I just want your help, Doctor.”

“But it’s going to -”

“Are you arguing with me?”

“_NO! _No, I-”

“Because really dear, you’re just making this take much longer than it needs to,” the boss monster smiled at him pleasantly, despite Gaster’s babbling to the contrary, that no, no _never _he didn’t want this to go on _any _longer, “Now… I won’t ask again, final answer.”

The monster pressed a little harder against Gaster’s back, a reminder to keep his eyes trained inside the room, on that little box now soot-stained inside, and on Grillby still flickering lower and lower.

“Will you help me with my little barrier project?”

“Yes! Yes I’ll help! I’ll do anything you ask!”

“No arguing? I know what I’m doing Doctor, trust me. I haven’t lied to you yet, have I?”

“N-n-n-no of course you haven’t,” and Gaster had no idea if the monster ever had or not. They’d never rightly spoken before that he could remember. Only ever seen from a hazy distance, dressed in black and giving orders. Only ever heard by word of mouth through bickering henchmen and third-party message givers. But that didn’t matter. Not right _now_.

“There, now was that so hard?” the monster asked, and his hand slipped from Gaster’s shoulders. And in a blink the monster was in the other room, gone one minute and with a sudden stroke he was simply _there _standing beside Grillby’s glass casket with those two strong-arm henchmen gathered close by his sides. 

But the monster didn’t open the case. Not yet. He just… stood there, watching. That coy smile still wrapped around his teeth. 

“You know,” he said quietly, and Gaster could barely hear him, “I like you much better in there. You kill a lot fewer of my men that way.”

He leaned down over the coffin, watching quizzically the fire within that still seemed to be looking past him at the ceiling above, “Maybe I should leave you in there, hmm? What say you?”

“Don’t!” Gaster screamed.

“I wasn’t talking to you, Doctor,” the monster wrapped his knuckles against the glass, “Hmm? Paying attention?”

Grillby punched the glass, a motion swift and sharp and sudden, and inches away from the boss monster’s face. It was a solid, loud, _sharp _sound, loud enough to make Gaster jump so hard he nearly fell off his feet. Loud enough to startle the guards in the room. Loud and fast enough to make the boss monster flinch back a step, the feathers of his mane fanned in a burst of color. And with mounting horror, Gaster watched as Grillby _laughed_. Heedless of his plight, of his coffin, of everything about his situation. He grinned and he laughed, coughing smoke and embers. And as the boss monster gathered himself together in a mighty snarl, Grillby said simply:

“You take yourself way too seriously.”

There was a moment where time seemed almost to freeze itself. Where every bitter ounce of the boss monster’s intent focused itself on the laughing elemental, where that smile was wiped off his face _finally _and set in an expression of fury. And where Gaster was too mortified to breathe.

The monster suddenly pounced forward, toppling the box with a mighty shove, breaking the hinge and cracking the glass. The lid opened and Grillby spilled out of it, coughing and wheezing as the air suddenly came rushing back to him. He curled on the floor, choking on his own breathing, unable to move as the boss monster glided towards him. And still, hoarsely, Grillby chuckled, bitter and cruel and defiant as the creature lifted him into the air, clawed hand clasped tight around the elemental’s throat, and slammed him against the nearby wall.

Gaster suddenly realized he was speaking, muttering under his own breath stupid fearful phrases. No and stop and _please _and so many other useless words that were so winced and stammered in his panic that they hardly were words at all. And scrabbled at the glass and his magic shook the air and he could do _nothing_. Trapped in this _stupid _room while Grillby, his Grillby was in _there _half choked and alone and staring down what Gaster could only see as hell itself.

But Grillby, oh Grillby. Resolute Grillby. Strong, incorrigible, reckless, _Grillby_. He didn’t _look _afraid. No, he was still grinning. His own slimy grin to match the one he’d stolen off the boss monster’s face even while his bound hands clutched at the sleeve of the creature’s tailored jacket and his feet searched for ground that was just _inches _too far away. 

With a strained voice still tainted with cruel laughter Grillby smiled, “You’re going to kill your leverage, sir. And then you’ll have nothing left.”

The feathers on the boss monster’s neck bristled with anger, and his grip on the elemental’s throat tightened. And there was a long moment where Gaster was sure this was it. Grillby had gotten himself killed. Gaster was going to watch Grillby get himself killed.

And then the monster dropped him, letting the elemental crumple into a coughing, choking heap on the floor. And Gaster dropped with him, relief making his knees buckle, and finally _finally _forcing tears to trace down his face. He watched Grillby, refused to take his eyes off him, as if he would blink and the boss monster would change his mind and dust the fire on the spot. But instead, the pair of henchmen picked up Grillby with an arm around each of his, and they dragged the dull, sputtering flame from the room while Gaster watched and wept, and he didn’t know if it was happiness or fear or a thousand other things that kept him slumped to the ground there pitifully.

Eventually he was taken out as well and marched back the direction he’d come; back into that cold cement cell with its metal bars that were too high above the melting point of Grillby’s fire. Back where just the night before he’d been crying and shaking and _sure, _so so _sure_, that Grillby was going to die today. And Grillby was in his cell as well, disheveled and slumped against the wall and still coughing, but _alive_.

“Are you okay?” Gaster asked frantically the moment they were alone, “Grillby? Grillby are you-”

“I told you not to do that.”

His voice was hoarse and soft and dreadfully quiet. Dissonantly so, compared to how loud and defiant he’d seemed just moments before.

“I… I’m sorry,” Gaster stammered, wiping at his eyes, “I’m sorry I… I couldn’t - I’m not… Grillby I’m not like you I’m sorry.”

He wiped at his eyes with a little more fervor, frustrated that he was crying again. He’d _just _managed to calm himself as he’d entered his cell, and he was exhausted, and he was crying _again_. Proving how wide the rift between him and Grillby was when it came to this. To everything about this.

“I know you’re not,” Grillby said, clearing his throat and rubbing his neck painfully. Gaster wanted to run to him and heal him somehow, a gentle touch of magic against his flame - but these damn cells and their damn bars -

“It’s okay, Gaster.”

Gaster. _Gaster_. He’d called him _Gaster_.

The skeleton blinked at him pitifully, his train of thought completely derailed by so simple a thing. And Grillby looked back at him and said with a voice so full of emotion it nearly hurt, “Are you alright?”

Gaster laughed at the absurdity of the question, “Am _I _alright? Am _I?”_

Grillby smirked at him, a smile that looked pitifully relieved, “I’ve still got to protect you, don’t I?”

“Gods above -”

“It’s a shame too,” Grillby sighed roughly, finally managing to prop himself up a little straighter against the wall, “That guy had such a nice suit.”

Gaster tilted his head to the side questioningly, “His… suit?”

“Yeah, top dollar. Cufflinks too,” Grillby held out two of his fingers, a pair of tiny silver links flashing against the color of his flame as he offered Gaster the most wicked, mischievous grin the skeleton had ever seen, “And you know, I bet they’re just the right melting point. I could make something neat with this, don’t you think? Oh, it’d have to be small though. A bobby pin or… a lockpick?”


End file.
